Underwater craft provide opportunities for scientific exploration and for individuals to view oceans and marine life. Although various types of passenger and operator compartments and various forms of hatches and sealing mechanisms can be used, a full acrylic cabin with an upper and lower hemisphere provides the best visibility for the passenger. In this type of cabin, the entire upper hemisphere can be used as a hatch, which allows easy entry and exit from the cabin and greater control of cabin temperature and humidity.
Assemblies for full acrylic cabins generally comprise two hemispheres mounted on one or more metallic rings. All structural attachments are made to the metal rings, leaving the acrylic windows clear for passenger viewing. The hemispheres typically are mounted onto the rings by incorporating an equatorial flange into each hemisphere and holding the hemispheres down on the ring by a retainer ring installed on top of the flange. While this type of mechanism could be used for underwater craft rated for deeper submersion, it would substantially reduce visibility for the passengers. This is because deeper rated submersibles require thicker acrylic domes and thicker equatorial flanges, which would in turn require the metal mounting ring height to increase proportionally. The resulting higher rings would reduce visibility from the cabin.
Attempted solutions include dome assemblies using various flangeless sealing mechanisms. Known methods of holding down flangeless domes can effectively seal spherical windows of 90° or 120° using a large retainer ring near the base. However, such systems suffer from the disadvantage of reduced visibility when used with 180° domes. This is because the retainer ring cannot be near the base as this does not provide sufficient axial restraint and requires a mechanical system to hold a retainer ring further up the window towards the apex.
Other known systems that use retainer rings for acrylic windows also have disadvantages. One such system uses a compounded window system holding a NEMO type window in place with a tie-rod system, together with a secondary tie-rod system holding down a hyper-hemisphere. This system is inherently unstable and provides only marginal control over the window when exposed to compressive, thermal, lateral or vertical loading. It is very difficult to maintain preload on the window because it has to rely on the stability of the tie rods. Tie rods often need to have a separate spring system to maintain sufficient tension. Moreover, this tie-rod arrangement becomes obstructive for viewing when a 180° hemispherical dome is used. Other known systems for a large hemispherical dome use a series of belts or a bridge system and a contact point at the apex to hold down the acrylic window. However, both of these systems have the drawback of a significantly obstructed view.
Therefore, there exists a need for a system that can provide a sealing mechanism for full acrylic cabins that imparts sufficient stability for underwater craft rated for deeper submersion. There is a further need for a sealing mechanism for full acrylic cabins that does not compromise cabin visibility by increasing mounting ring height. Specifically, there is a need for a flangeless sealing mechanism for full acrylic underwater craft cabins that uses an entire upper hemisphere as a hatch and maintains good cabin visibility.